The present invention relates to a surface treatment method and an optical part, and particularly to a surface treatment method utilizing atmospheric pressure plasma and an optical part treated thereby.
For example, an optical part formed by injection molding of a resin material is mounted on a precision optical instrument such as an optical pick-up device so as to exhibit optical functions of high precision. In such an optical part, there are some provided with fine roughness such as a diffraction grating of a ring band form on the optical plane, to exhibit higher optical functions.
In case of forming such as an anti-reflection film on an optical part, heretofore, a thin film is formed on an optical plane by adhesive deposition of particles for film formation by means of such as a vacuum evaporation method and a sputtering method. However, in case of performing a deposition treatment on an optical part material of which an optical plane is provided with fine roughness, there are problems described below according to a vacuum evaporation method and a sputtering method.
FIG. 3 shows a partial cross section of a lens of which a sawtoothed ring band diffraction structure of an optical plane was subjected to deposition, and such as film thickness is shown exaggeratedly. As shown in the drawing, when there is sawtoothed roughness on the plane on which film is to be deposited, film thickness made of particles deposited thereon generates unevenness due to various reasons such as difference of an incidence angle of particles to the deposition plane and obstruction by the convex portions to particles to proceed toward the concave portions. When such unevenness of film thickness is generated, there may be caused discrepancies between a produced part form and a designed form resulting in that even an optical part having excellent optical characteristics in a designed stage possibly cannot exhibit satisfactory optical characteristics as a practical product. Further, inherent functions of a thin film (such as an anti-reflection function) possibly are not exhibited sufficiently.
For these manufacturing problems, heretofore, a device, in which by rotating an optical part on which film is to be deposited or a jig to hold the part so as to perform more uniform deposition on an optical plane, is provided, however, it has been difficult to form a sufficiently uniform film without deteriorating the capabilities. Further, in such a deposition treatment according to conventional techniques, there have been problems in that a device to rotate an optical part or a jig, and a space for rotation are required, and that a number of optical parts treated at one time becomes small resulting in poor treatment efficiency. Further, in case of vacuum evaporation, because apparatuses such as a closed vessel and an exhausting apparatus have to be set due to an optical part being necessarily placed in vacuum surrounding, there caused cost increase in addition to handling inconvenience.